Bruno Rossaro

A reference river system for the Alps: the ‘Fiume Tagliamento’

A major deterrent to a full understanding of the ecological ramifications of river regulation at the catchment scale is a lack of fundamental knowledge of structural and functional attributes of morphologically intact river systems. For example, both the River Continuum and the Serial Discontinuity Concepts, in their original formulations, had the implicit assumption of a stable, single-thread channel from headwaters to the sea. The Fiume Tagliamento traverses a course of 172 km from its headwaters in the Italian Alps to the Adriatic Sea. No high dams impede the rivers passage as it flows through the characteristic sequence of constrained, braided, and meandering reaches. The Tagliamento, the only large morphologically intact Alpine river remaining in Europe, provides insight into the natural dynamics and complexity that must have characterized Alpine rivers in the pristine state. The Tagliamento has a flashy pluvio-nival regime (mean Q=109 m3 s-1, with flood flows up to 4000 m3 s-1). Thousands of newly-uprooted trees were strewn across the active bed and floodplain along the rivers course following a major flood in the autumn of 1996. The active floodplain is up to 2 km wide and contains a riparian vegetation mosaic encompassing a range of successional stages. Up to 11 individual channels per cross section occur in the braided middle reaches. Islands are a prominent feature of the riverine landscape and island dynamics are postulated to play a key role in determining pattern and process across scales. Future studies will examine the roles of island dynamics and large woody debris in structuring biodiversity patterns of aquatic biota and successional trajectories of riparian vegetation. The high levels of spatiotemporal heterogeneity exhibited by the Fiume Tagliamento provide a valuable perspective for regulated river ecologists and those engaged in conservation and restoration.

Microdistribution of chironomids (Diptera: Chironomidae) in Alpine streams: an autoecological perspective

Chironomid communities from three glacial and three non-glacial high mountain streams in three Alpine river basins were analyzed (Conca, Niscli, Cornisello, NE Italy, 46° N, 10° E). Eighteen sampling reaches belonging to five stream types (kryal, subkryal, glacio-rhithral, kreno-rhithral, outlet) were investigated. At each reach, geomorphological, physical, chemical and biological data were collected. Field surveys were carried out during three periods per year from 1996 to 1998: immediately after spring snowmelt, in mid-summer and in early autumn. In all, 439 zoobenthos samples were collected from 5 to 10 microhabitats of 0.1 m2 in each reach and date using a standard pond net (mesh size of 250 μm). About 50% of individuals collected were chironomids (26 673 specimens, 53 taxa), with densities ranging from 4 to 2652 ind m−2. With few exceptions, they dominated as number of taxa and individuals in all reaches. Chironomid subfamilies Diamesinae and Orthocladiinae were most abundant, especially in glacial reaches, where Diamesa spp. constituted up to 100% of the total fauna. Chironomid distribution was analyzed in relation to 37 abiotic variables, referring to stream origin, hydrology, geomorphology, physics and chemistry. Diamesa steinboecki, D. latitarsis gr. A and Pseudokiefferiella parva were the taxa best associated with ‘glacial’ conditions (i.e. high channel instability or presence of bedrock, high suspended solids and total phosphorous content, low conductivity and silica content, highly variable diel discharge and low mean temperature), while Pseudodiamesa branickii, Corynoneura spp., Eukiefferiella spp., Parorthocladius nudipennis, Tvetenia calvescens/bavarica, Thienemaniella spp. and Micropsectra atrofasciata were mostly associated with ‘non-glacial’ conditions. Substratum particle size, water depth, current velocity, the presence of riffles/pools and of mosses/algae (Hydrurus foetidus) were the major factors affecting microdistribution of chironomids in the investigated streams.

Collective Behaviour without Collective Order in Wild Swarms of Midges

Collective behaviour is a widespread phenomenon in biology, cutting through a huge span of scales, from cell colonies up to bird flocks and fish schools. The most prominent trait of collective behaviour is the emergence of global order: individuals synchronize their states, giving the stunning impression that the group behaves as one. In many biological systems, though, it is unclear whether global order is present. A paradigmatic case is that of insect swarms, whose erratic movements seem to suggest that group formation is a mere epiphenomenon of the independent interaction of each individual with an external landmark. In these cases, whether or not the group behaves truly collectively is debated. Here, we experimentally study swarms of midges in the field and measure how much the change of direction of one midge affects that of other individuals. We discover that, despite the lack of collective order, swarms display very strong correlations, totally incompatible with models of non-interacting particles. We find that correlation increases sharply with the swarms density, indicating that the interaction between midges is based on a metric perception mechanism. By means of numerical simulations we demonstrate that such growing correlation is typical of a system close to an ordering transition. Our findings suggest that correlation, rather than order, is the true hallmark of collective behaviour in biological systems.

Chironomids from Southern Alpine running waters: ecology, biogeography

The chironomid fauna living in running waters in the Southern Alps was investigated from an ecological and biogeographical point of view: 202 species were identified (not including terrestrial species). It must be emphasised that species identification is tentative within some genera, especially those awaiting revision (e.g., Boreoheptagyia, Chaetocladius). Although much taxonomic work was done in the past on the chironomid Alpine fauna, there are still many unsolved problems. Most of the species found are widespread in the Palearctic Region, with no evidence of bio-geographical barriers separating different Alpine sectors. Really a relatively high number of species reported from the northern and western side (France, Switzerland, Austria) of the Alps was not captured on the southern side (Italy), whereas most species found on the southern side are also present on the northern one. Very few species are reported from southern side only. Lack of sampling, imperfect taxonomic knowledge and different environmental conditions between the northern and southern sides may be responsible of this result. A comparison of the fauna of the southern Alps with the fauna of the Apennines suggests that the differences are probably more related to ecological conditions (lack of glaciers in the Apennines) than to biogeographical barriers. Different chironomid assemblages colonise manifold habitat types: strict cold-stenothermal species tolerating high current velocity (e.g., Diamesa latitarsis – steinboecki group) are almost the sole inhabitants of kryal biotopes, while other cold-stenothermal species are restricted to cold springs (Diamesa dampfi, D. incallida, Tokunagaia rectangularis, T. tonollii), there are also species characteristic of hygropetric habitats (Syndiamesa edwardsi, S. nigra) or restricted to lacustrine habitats (Corynoneura lacustris, Paratanytarsus austriacus). It must be emphasised that different responses to environmental factors can be observed between species belonging to the same genus (e.g., Diamesa, Eukiefferiella, Orthocladius , Paratrichocladius), so species identification is really needed for a good ecological work. Water temperature, current velocity, substrate type are the most critical factors, sometime chironomid species appear to be rather opportunistic and their presence or absence cannot be clearly related to a well defined range of values of environmental variables: be it a lack of knowledge or a real datum will be the task of future studies. The waters of the Alps are still relatively unpolluted, but hydraulic stress due to river damming and canalization is a serious problem for macrofauna conservation, and as the glaciers retreat, the species confined to the glacial snouts are at risk of extinction, some of them possibly even before their existence be discovered.

Landscape–stream interactions and habitat conservation for amphibians

Semiaquatic organisms depend on the features of both water bodies and landscapes; the interplay between terrestrial and aquatic systems might influence the semiaquatic communities, determining the scale at which management would be more effective. However, the consequences of such interplay are not frequently quantified, particularly at the community level. We analyzed the distribution of amphibians to evaluate whether the influence of landscape features on freshwater ecosystems can have indirect consequences at both the species and community level. We surveyed 74 streams in northern Italy to obtain data on breeding amphibians, water, and microhabitat features; we also measured features of surrounding landscapes. We used an information-theoretic approach and structural equation models to compare hypotheses on causal relationships between species distribution and variables measured at multiple levels. We also used a constrained redundancy analyses to evaluate causal relationships between multivariate descriptors of habitat features and community composition. Distribution of Salamandra salamandra was related to landscape, hydrological, and water characteristics: salamanders were more frequent in permanent streams with low phosphate concentration within natural landscapes. Water characteristics were dependent on landscape: streams in natural landscapes had less phosphates. Landscape influenced the salamander both directly and indirectly through its influence on phosphates. Community structure was determined by both landscape and water characteristics. Several species were associated with natural landscapes, and with particular water characteristics. Landscape explained a significant proportion of variability of water characteristics; therefore it probably had indirect effects on community. Upland environments play key roles for amphibians, for example, as the habitat of adults, but upland environments also have indirect effects on the aquatic life stages, mediated through their influence on water characteristics. Synergistic effects can magnify the negative consequences of landscape alteration on amphibians; landscape management can be particularly effective, as it can also improve wetland features.

Environmental features influencing Carabid beetle (Coleoptera) assemblages along a recently deglaciated area in the Alpine region

Abstract 1. The spatio‐temporal approach was used to evaluate the environmental features influencing carabid beetle assemblages along a chronosequence of an Italian Alpine glacier foreland. The influence of environmental variables on species richness, morphology (wing and body length), and distribution along the chronosequence was tested.

Epigean Arthropod Succession along a 154-year Glacier Foreland Chronosequence in the Forni Valley (Central Italian Alps)

Abstract The 154-year (1850–2004) chronosequence of the Forni Glacier foreland has been studied by sampling ant, centipede, ground beetle, and spider species assemblages. Species numbers increase with terrain age along the chronosequence from 2 to 26 on the oldest soils. Thirty-nine species were collected; species richness and diversity (Shannons Index) of communities are correlated to the year of soil deglaciation. Shannon Index values increase with sites deglaciated between 1 and 61 years ago; sites deglaciated between 61 and 78 years ago produce similar values, and those deglaciated 78 to 154 years ago show a further increase in diversity. Ground beetles and spiders are found at all sites, while ants and centipedes were associated with mature forest soils. On the glacier surface, pioneer species such as the wolf-spider Pardosa saturatior and the ground beetle Oreonebria castanea permanently inhabit the supraglacial detritus surviving on trophic resources. Wingless ground beetle species are associated with mature soils, especially those with high hydric stability. Open land species typical of primary succession are found in the pioneer and intermediate stages, while community assemblages found on older terrain are linked to forest vegetation structure and dynamics.

Modelling lake macroinvertebrate species in the shallow sublittoral: relative roles of habitat, lake morphology, aquatic chemistry and sediment composition

Macroinvertebrates are one of the key components of lake ecosystems and are required to be monitored alongside other biological groups to define ecological status according to European Union legislation. Macroinvertebrate communities are highly variable and complex and respond to a diverse series of environmental conditions. The purpose of this study was to examine the relative importance of environmental variables in explaining macroinvertebrate abundance. A total of 45 sub-alpine lakes were sampled for macroinvertebrates in the shallow sublittoral. Environmental variables were grouped into four types: (1) aquatic physical and chemical parameters, (2) littoral and riparian habitat, (3) lake morphometric parameters and (4) sediment chemical characteristics. Nonparametric multiplicative regression (NPMR) was used to model the abundance of individual macroinvertebrate taxa. Significant models were produced for nine out of the 24 taxa examined. Sediment characteristics were the group most frequently included in models and also the factors to which taxa abundance was the most sensitive. Aquatic physical and chemical variables were the next group most frequently included in models although chlorophyll a was not included in any of the models and total phosphorus in only one. This indicates that many taxa may not show a direct easily interpretable response to eutrophication pressure. Lake morphometric factors were included in several of the models although the sensitivity of macroinvertebrate abundance tended to be lower than for sediment and aquatic physical and chemical factors. Habitat factors were only included in three models although riparian vegetation was found to have a significant influence on the abundance of Ephemera danica indicating that ecotone integrity is likely to play a role in its ecology. Overall, the models tended to be specific for species with limited commonality across taxa. Models produced by NPMR indicate that the response of macroinvertebrates to environmental variables can be successfully described but further research is required focussing in more detail on the response of key taxa to relevant environmental parameters and anthropogenic pressures.

Contrasting chironomid assemblages in two high Arctic streams on Svalbard

Chironomid communities were investigated twice in summer 1997 in a glacier-fed (Bayelva) and a non-glacial stream (Londonelva), fed by snowmelt and rainfall near Ny-Alesund (Svalbard Archipelago, 78°N). Environmental conditions (discharge, water temperature, suspended sediment) were harsher for the fauna in the glacial system than in the non-glacial one. In all, 29 chironomid species were identifi ed from larval, pupal and male adult material, including six species new to Svalbard. Diamesa was the best represented genus, showing contrasting distributional trends at the species level in the two streams: Diamesa aberrata and D. bohemani were more characteristic of the glacial stream, while D. arctica and D. bertrami colonised primarily the snowmelt-fed one. Total abundance of chironomid larvae was ten times greater in Londonelva than in Bayelva. The prevailing harsh conditions in glacial streams, such as high and fl uctuating discharge, high sediment transport and substrate instability, strongly infl uenced the abundance of the chironomid fauna, demonstrating the key importance of water source in Arctic streams.

Potential role of island dynamis in river ecosystems

Islands and mid-channel bars are characteristic features of alluvial rivers that have been intensively investigated by fluvial geomorphologists (e.g. KNIGHTON 1984, ScHUMM 1985, CHURCH 1992). The ro le o f island dynamics, however, has been given scant attention by stream ecologists, perhaps reflecting the virtual elimination of islands from managed rivers. For example, of the ca. 2,000 vegetated islands historically present in the Austrian Danube, only six remain. The few islands that remain in artificially constrained rivers (THORP 1992) have lost their dynamic attributes. Because islands are a dominant feature of pristine alluvial rivers, a better understanding o f the ecological ro le o f island dynamics has the potential of providing new insight into functional attributes of lotic ecosystems, with important implications for biodiversity and river conservation. The ensuing material is derived from a preliminary investigation of islands in an Alpine river system, employing field studies in conjunction with detailed analyses of maps and aerial photographs. The distribution, abundance and size frequency of islands along the river continuum are presented. Based on those data, we propose the development of an island dynamics paradigm to provide a novel perspective for holistic studies that should lead to a broader understanding of lotic ecosystems.